1. Field of the Invention
The present invention generally relates to surgical device. More specifically, the present invention relates to bio-absorbable surgical devices, including implantable devices for fixating bone and tissue and non-implantable surgical devices.
2. Related Technology
The overall market for orthopedic implants is large at $43 B p.a. worldwide (2012 estimate, Frost and Sullivan) with $14 B p.a. for reconstruction devices and $4 B p.a. for trauma fixation devices. In the U.S., over 2.5 million implant and ligament repair procedures are performed annually. Ligament repair procedures alone have been estimated to be greater than 700,000 p.a. In smaller countries, such as in Germany, there are over 500,000 p.a. that require fixation with surgical bone implants. Of these, 300,000 or so need rescission surgery to remove the implants, at a cost of $700 MM p.a. The cost of U.S. DOD secondary removal operations is estimated at $500 MM p.a. The health system savings in fostering faster recovery and the avoidance of infection and inflammation treatments with a new technology could be very significant.
Surgeons need more effective measures to correct ligament and bone damage, such as those which occur in shoulder lesions, anterior cruciate ligaments, hamstrings and bone fractures of various types, including craniofacial fractures. Currently, a wide variety of techniques are used in these reparative surgeries, including permanent non-absorbable implants, temporary non-absorbable implants and bio-absorbable polymer implants.
A gradual load transfer from an implant to the healing bone and tissue is desired in these reparative surgeries. Permanent metal fixation devices or implants, while strong, do not allow for the proper loading of the fixated bones to enable them to sufficiently regrow. Plastic fixation devices fall short of mimicking bone properties. Neither type of fixation device affords the gradual transfer of loading. Metal fixation devices further also interfere with post-operative magnetic resonance imaging (MRI) scanning, and in some instances, the fixation devices require subsequent surgeries for removal of the fixation device. There is lost productive time, physiological harm, threat of infection and pain that results from secondary operations to remove the fixation devices, particularly in the removal of craniofacial fixation devices and those from ligaments and small bones, such as those in the hands, toes and ankles. The needing cost associated with such removals is extensive.
Biodegradable plastics are also sometimes used as the fixation devices to allow repaired ligaments to heal and strengthen. As noted above, such plastic fixation devices do not properly mimic bone characteristics in terms of strength. Nor do these polymer implants encourage bone growth on their receding surface as they absorb. Stronger, tougher and stiffer materials in the current biodegradable plastics are needed for these procedures.
In many surgical procedures, metal instruments, such as retractors, are commonplace. During their use, it is possible that metal fragments are formed and accidentally left in the body of the patient as the surgery site is closed up. If the retractors are fabricated from a noncorrosive material, such as stainless steel and titanium, these metal fragments can be damaging to organs.
From the above, it is seen that implants and retractors, of a strong, tough, and dissolvable metal, are needed.
At the same time, non-toxicity to the human body is of paramount importance for implants. As an example of concerns, the most common alloying element for magnesium (Mg) base alloys to add strength and corrosion resistance is aluminum (Al); yet the presence Al in the Mg alloy implants raises serious concerns regarding Al's possible effects on dementia and Alzheimer's disease. Other potential Mg implants contain Rare Earth (RE) elements for strengthening; but the composition of additive RE master alloys is variable, containing a mixture of RE elements—some RE elements being non-toxic and some being toxic. Also, RE elements tend to concentrate at the dissolving implant site; not being carried away by body functions as Mg is. An alloy base and its alloying elements need to meet the following requirements of non-toxicity: minimal gas bubbling around the implant; normal hematology and serum biochemistry; good osteoconductivity and osteoinductivity; enhanced attached new bone growth of improved density and strength; good cytocompatibility; non-inflammation; good adhesion of osteoblasts; even distribution of alloying elements around the implants; and the addition of essential nutrients to the body, but not exceeding yearly safe limits.
Thus, a new alloying concept is needed to regain the strength lost by removing Al while improving toughness and optimizing corrosion rate; but not exceeding the yearly safe limits on toxicity.